# CVE-2020-15656: Firefox ESR and 2 others: JIT optimizations involving the Javascript arguments object could confuse later optimizations. CVE-2020-15656 is fixed in 11 products on 2 platforms, first by Mozilla Thunderbird (en-US) 78.1.0, released July 29, 2020. It is not reported as exploited. Patch Radar priority: High. - Web page: https://patchblox.com/security/cve/CVE-2020-15656 - Priority: High - CVSS: 8.8 (Important) - EPSS: 0.0152 - CISA KEV: not listed - Exploited (vendor report): no - Publicly disclosed: no - Published: Jul 28, 2020 - Vendor advisory: https://nvd.nist.gov/vuln/detail/CVE-2020-15656 ## Description JIT optimizations involving the Javascript arguments object could confuse later optimizations. This risk was already mitigated by various precautions in the code, resulting in this bug rated at only moderate severity. This vulnerability affects Firefox ESR < 78.1, Firefox < 79, and Thunderbird < 78.1. ## Where it's fixed | Platform | Product | Fixed in | Fix | Released | |---|---|---|---|---| | Windows apps | Mozilla Firefox ESR (en-US) | 91.0 | [Mozilla Firefox ESR (en-US) 91.0](https://patchblox.com/security/data/fix/windows-app/mozilla.firefox.esr-91.0.md) | Aug 4, 2021 | | Windows apps | Mozilla Thunderbird (en-US) | 78.1.0 | [Mozilla Thunderbird (en-US) 78.1.0](https://patchblox.com/security/data/fix/windows-app/mozilla.thunderbird-78.1.0.md) | Jul 29, 2020 | | Linux | firefox RHEL 8 | 0:78.2.0-2.el8_2 | [RHSA-2020:3557](https://patchblox.com/security/data/fix/linux/rhsa-2020-3557.md) | Aug 26, 2020 | | Linux | firefox Ubuntu 18.04.6 LTS (bionic) | 79.0+build1-0ubuntu0.18.04.1 | [firefox 79.0+build1-0ubuntu0.18.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-firefox-79.0-build1-0ubuntu0.18.04.1.md) | Aug 10, 2020 | | Linux | firefox Ubuntu 20.04 LTS (focal) | 79.0+build1-0ubuntu0.20.04.1 | [firefox 79.0+build1-0ubuntu0.20.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-focal-firefox-79.0-build1-0ubuntu0.20.04.1.md) | Aug 10, 2020 | | Linux | firefox ol 8 | 0:78.2.0-2.0.1.el8_2 | [ELSA-2020-3557](https://patchblox.com/security/data/fix/linux/elsa-2020-3557.md) | Aug 28, 2020 | | Linux | firefox-geckodriver Ubuntu 18.04.6 LTS (bionic) | 79.0+build1-0ubuntu0.18.04.1 | [firefox-geckodriver 79.0+build1-0ubuntu0.18.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-firefox-geckodriver-79.0-build1-0ubuntu0.18.04.1.md) | Aug 10, 2020 | | Linux | firefox-geckodriver Ubuntu 20.04 LTS (focal) | 79.0+build1-0ubuntu0.20.04.1 | [firefox-geckodriver 79.0+build1-0ubuntu0.20.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-focal-firefox-geckodriver-79.0-build1-0ubuntu0.20.04.1.md) | Aug 10, 2020 | | Linux | firefox-mozsymbols Ubuntu 18.04.6 LTS (bionic) | 79.0+build1-0ubuntu0.18.04.1 | [firefox-mozsymbols 79.0+build1-0ubuntu0.18.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-firefox-mozsymbols-79.0-build1-0ubuntu0.18.04.1.md) | Aug 10, 2020 | | Linux | firefox-mozsymbols Ubuntu 20.04 LTS (focal) | 79.0+build1-0ubuntu0.20.04.1 | [firefox-mozsymbols 79.0+build1-0ubuntu0.20.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-focal-firefox-mozsymbols-79.0-build1-0ubuntu0.20.04.1.md) | Aug 10, 2020 | | Linux | thunderbird Ubuntu 18.04.6 LTS (bionic) | 1:78.8.1+build1-0ubuntu0.18.04.1 | [thunderbird 1:78.8.1+build1-0ubuntu0.18.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-thunderbird-1-78.8.1-build1-0ubuntu0.18.04.1.md) | Apr 22, 2021 | | Linux | thunderbird Ubuntu 20.04 LTS (focal) | 1:78.7.1+build1-0ubuntu0.20.04.1 | [thunderbird 1:78.7.1+build1-0ubuntu0.20.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-focal-thunderbird-1-78.7.1-build1-0ubuntu0.20.04.1.md) | Jan 25, 2021 | | Linux | thunderbird-gnome-support Ubuntu 18.04.6 LTS (bionic) | 1:78.8.1+build1-0ubuntu0.18.04.1 | [thunderbird-gnome-support 1:78.8.1+build1-0ubuntu0.18.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-thunderbird-gnome-support-1-78.8.1-build1-0ubuntu0.18.04.1.md) | Apr 22, 2021 | | Linux | thunderbird-gnome-support Ubuntu 20.04 LTS (focal) | 1:78.7.1+build1-0ubuntu0.20.04.1 | [thunderbird-gnome-support 1:78.7.1+build1-0ubuntu0.20.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-focal-thunderbird-gnome-support-1-78.7.1-build1-0ubuntu0.20.04.1.md) | Jan 25, 2021 | | Linux | thunderbird-mozsymbols Ubuntu 18.04.6 LTS (bionic) | 1:78.8.1+build1-0ubuntu0.18.04.1 | [thunderbird-mozsymbols 1:78.8.1+build1-0ubuntu0.18.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-thunderbird-mozsymbols-1-78.8.1-build1-0ubuntu0.18.04.1.md) | Apr 22, 2021 | | Linux | thunderbird-mozsymbols Ubuntu 20.04 LTS (focal) | 1:78.7.1+build1-0ubuntu0.20.04.1 | [thunderbird-mozsymbols 1:78.7.1+build1-0ubuntu0.20.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-focal-thunderbird-mozsymbols-1-78.7.1-build1-0ubuntu0.20.04.1.md) | Jan 25, 2021 | | Linux | xul-ext-calendar-timezones Ubuntu 18.04.6 LTS (bionic) | 1:78.8.1+build1-0ubuntu0.18.04.1 | [xul-ext-calendar-timezones 1:78.8.1+build1-0ubuntu0.18.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-xul-ext-calendar-timezones-1-78.8.1-build1-0ubuntu0.18.04.1.md) | Apr 22, 2021 | | Linux | xul-ext-calendar-timezones Ubuntu 20.04 LTS (focal) | 1:78.7.1+build1-0ubuntu0.20.04.1 | [xul-ext-calendar-timezones 1:78.7.1+build1-0ubuntu0.20.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-focal-xul-ext-calendar-timezones-1-78.7.1-build1-0ubuntu0.20.04.1.md) | Jan 25, 2021 | | Linux | xul-ext-gdata-provider Ubuntu 18.04.6 LTS (bionic) | 1:78.8.1+build1-0ubuntu0.18.04.1 | [xul-ext-gdata-provider 1:78.8.1+build1-0ubuntu0.18.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-xul-ext-gdata-provider-1-78.8.1-build1-0ubuntu0.18.04.1.md) | Apr 22, 2021 | | Linux | xul-ext-gdata-provider Ubuntu 20.04 LTS (focal) | 1:78.7.1+build1-0ubuntu0.20.04.1 | [xul-ext-gdata-provider 1:78.7.1+build1-0ubuntu0.20.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-focal-xul-ext-gdata-provider-1-78.7.1-build1-0ubuntu0.20.04.1.md) | Jan 25, 2021 | | Linux | xul-ext-lightning Ubuntu 18.04.6 LTS (bionic) | 1:78.8.1+build1-0ubuntu0.18.04.1 | [xul-ext-lightning 1:78.8.1+build1-0ubuntu0.18.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-xul-ext-lightning-1-78.8.1-build1-0ubuntu0.18.04.1.md) | Apr 22, 2021 | | Linux | xul-ext-lightning Ubuntu 20.04 LTS (focal) | 1:78.7.1+build1-0ubuntu0.20.04.1 | [xul-ext-lightning 1:78.7.1+build1-0ubuntu0.20.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-focal-xul-ext-lightning-1-78.7.1-build1-0ubuntu0.20.04.1.md) | Jan 25, 2021 | --- Data as of 2026-11-08T00:53:09Z UTC. 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